This invention relates to an exposure value control apparatus designed to prevent uneven exposure in an electrostatic copier of the slit exposure type.
In the conventional photocopiers having means for lightening the original by adjusting the projection lamp to thereby lighten the image of the original to be copied, which image is reflected and cast onto a photoconductive member after which the photoconductive member is exposed, it is difficult to assure that the light will evenly reach the photoconductive member. For example, the reflected lighted image generally results in being brighter at the central portion thereof than at its ends, as the light reaching the photoconductive member depends on the properties of the lens of the optical system.
For the purpose of preventing uneven exposure, the conventional exposure control system, designed to adjust the brightness of the image of the original has blades which are so shaped as to cut into the light path more at the central portion, or a masking is disposed in front of the projection lamp so that the loss of light at the ends might be compensated for by adjusting its position.
With these electrostatic copiers, the distribution of the exposure value varies from one to another depending on the comprehensive properties of their optical systems, photoconductive members, exposure lamps, etc.. This is attributable to uneven properties between the components of one copier and their counterparts of another. Therefore, the exposure must be adjusted when manufacturing each copier.
Accordingly, the aforementioned conventional exposure control system has been found ineffective because of its inability to provide a fine adjustment of the exposure which is different from one copier to another.